Bone positioning device and method

ABSTRACT

A method for positioning a bone cutting guide on a tibia may begin with coupling a bone cut positioning apparatus with a tibia. The method may also include adjusting the positioning apparatus in a varus/valgus orientation to shine a light emitted by a light emitter approximately along a midline of an anterior surface of the tibia, swinging a pivoting arm about a pivot joint to direct the emitted light along a medial surface of the tibia, adjusting the positioning apparatus in an anterior/posterior orientation to shine the light approximately along a midline of the medial surface, contacting a stylus with a proximal end of the tibia to select a cutting depth for a bone cut to be made on the tibia, and attaching the bone cutting guide to the tibia in a position determined by the positioning apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation in part of U.S. patent application Ser. No. 12/729,222, filed Mar. 22, 2010, which is a continuation in part of U.S. patent application Ser. No. 12/616,747, filed Nov. 11, 2009, which is a continuation of PCT/US2009/063015 filed Nov. 2, 2009, the full disclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Embodiments described herein relate to medical/surgical devices, systems and methods. More specifically, embodiments described herein relate to devices, systems and methods for enhancing a knee surgery procedure.

Approximately 550,000 total knee replacement surgeries (also referred to as total knee arthroplasty (“TKA”) are performed annually in the U.S. for the treatment of chronic knee pain and dysfunction. As the U.S. and world populations become older and more obese, knee replacement surgery will become even more common, as knee joints endure greater and greater wear and tear from their increased loads and years of stress. Conventional TKA surgery is often very effective but also very invasive and sometimes imprecise, thus leading to less than ideal outcomes.

The knee is generally defined as the point of articulation of the femur with the tibia. Structures that make up the knee include the distal femur, the proximal tibia, the patella, and the soft tissues within and surrounding the knee joint. Four ligaments are especially important in the functioning of the knee—the anterior cruciate ligament, the posterior cruciate ligament, the medial collateral ligament, and the lateral collateral ligament. In an arthritic knee, protective cartilage at the point of articulation of the femur with the tibia has been worn away to allow the femur to directly contact the tibia. This bone-on-bone contact causes significant pain and discomfort. The primary goals of a TKA procedure are to replace the distal end of the femur, the proximal end of the tibia, and often the inner surface of the patella with prosthetic parts to avoid bone-on-bone contact and provide smooth, well-aligned surfaces for joint movement, while also creating a stable knee joint that moves through a wide range of motion.

In a TKA surgery, the surgeon cuts open the knee, flips the patella bone out of the way, cuts bone from the distal end of the femur and from the proximal end of the tibia, and installs new, manmade, prosthetic ends onto the femur and tibia to form a new knee joint. In some TKA procedures, the interior surface of the patella may also be covered with a prosthetic. Cutting open the knee, moving the patella, sawing off bone segments, and implanting the manmade implants is a very invasive, though effective, procedure.

Determining how to cut the ends of the femur and tibia to ensure proper alignment and balancing of ligament tension in the new, prosthetic knee joint can be very challenging and often involves more art than science. An artificial knee joint in which the ligament tension is not well balanced endures significantly more wear and tear than one that is properly balanced, and yet, this proper balance is very difficult to achieve. As a consequence, TKA surgery performed on younger patients typically needs to be redone one or more times during the patient's life.

Due to the invasiveness and imprecision of traditional TKA, there is a need for improved techniques and devices in this field. A number of minimally invasive (or “less invasive”) TKA techniques, involving smaller incision sizes and reduced trauma to the patient have been developed in an effort to reduce patient recovery time. Some of these minimally invasive techniques, as well as other innovations, have also sought to enhance and/or facilitate TKA by making it more precise and repeatable and thus, ideally, reducing wear and tear on artificial knees and the need for repeat procedures. Improved techniques and devices would also mean enhanced outcomes for all TKA patients, with better functioning of the knee joint and longer useful life of the artificial knee.

One of the greatest challenges in TKA surgery is to properly balance ligament tension, especially in the medial and lateral collateral ligaments, through a full range of motion of the knee. The collateral ligaments, which connect the distal femur and proximal tibia on the medial and lateral aspects of the knee, account for much of the stability and movement of the knee. If one of the collateral ligaments is too lax or too tight relative to the other collateral ligament, the knee will typically be unstable, range of motion may be limited, the patella may move (or “track”) improperly, and the femur and/or tibia may wear unevenly, leading to arthritis and pain. Uneven ligament tension after TKA surgery will typically cause joint instability and poor patellar tracking, limited range of motion, and impaired function of the knee, as well as uneven, increased wear of the prosthetic device, which often necessitates repeat surgery. Thus, it is imperative for the short- and long-term success of a TKA procedure to achieve balanced ligament tension in the knee through a full range of motion.

Balancing ligament tension during TKA surgery is complicated by the fact that the natural knee does not operate like a hinge moving about a single axis. The knee exhibits dynamic external rotation of the tibia relative to the femur as the knee moves from its flexed to its fully extended position. This automatic rotation of the tibia occurs in the opposite direction when the knee is flexed from its fully extended position to produce an internal rotation of the tibia relative to the femur. Thus, the natural knee exhibits a rotary laxity that allows the tibia to rotate through a limited internal and external arc during knee flexion. In addition, the femur translates anteriorly and posteriorly as the tibia is being flexed about it, bringing yet another movement variable into the equation. Thus, the ligaments of the knee, along with the femur, tibia and patella, create a truly dynamic bio-mechanism, making ligament tension balancing in TKA surgery extremely challenging. This challenge is even greater in minimally invasive TKA procedures, in which incisions are smaller than those made in “open” TKA surgeries. Additionally, the incision made during minimally invasive TKA surgery is biased to the medial side, leaving the lateral side of specifically the distal femur “closed” to access of front or end loaded surgical instruments

One way surgeons try to balance ligament tension during TKA procedures is by cutting one or more ligaments to release tension from one part of the joint (“ligament release”). The disadvantage of ligament release, however, is that once a ligament is cut it cannot be regenerated, and the ligaments of the knee provide much needed stability to the knee joint.

Rather than or in addition to ligament release, the components of a total knee prosthesis may be selected and positioned to balance ligament tension. Since the femoral and tibial components of the knee prosthesis are attached to cut surfaces of the distal femur and proximal tibia respectively, placement and orientation of the femoral and tibial bone cuts are very important for balancing knee ligament tension. As with ligament release however, it is often very challenging to position the femoral and tibial bone cuts and prosthetic components to provide ideal ligament tension through the range of motion. This is due primarily to the complexity of motion about the knee, as described above, and the difficulty of assessing and making the bone cuts during the procedure to achieve desired ligament tension through the full range of motion.

Improved methods and apparatus for facilitating and/or enhancing femoral bone cuts have been described by the assignee of the present application in, for example, U.S. Pat. Nos. 7,578,821 and 7,442,196. Few if any innovations have been made, however, to facilitate or enhance tibial bone cuts in a TKA procedure.

To make a tibial cut in a typical TKA procedure, an orthopedic surgeon typically uses a cutting block or cutting guide temporarily attached to the front of the tibia via a rod that is typically attached to an ankle clamp at the distal end to the tibia (an extramedulary rod) and aligned approximately with the mechanical axis of the anterior surface of the tibia. The cutting block is used to guide a surgical saw blade or rotary tool in making the tibial bone cut. Positioning such a cutting block, therefore, is crucial to forming well-positioned bone cuts for attachment of the tibial and femoral prosthetic components. The tibial cut is the foundation of a TKA, as it affects the spacing, alignment and balance between the tibia and femur when the knee is in flexion (the flexion gap) the spacing, alignment and balance between the tibia and femur when the knee is in extension (the extension gap) and all points of articulation between extension and flexion.

Typically, the tibial component of a knee prosthesis is positioned on a flat, horizontal cut surface of the proximal tibia (at a 90 degree “varus/valgus” angle relative to the long axis of the tibia), and the position and orientation of the tibial component typically do not vary greatly from knee to knee. However, by making a cut on the tibia at 90 degrees to the long axis of the bone, a bigger space is created laterally than medially, due to the tibia's natural approximately 3 degrees of varus slope. Furthermore, the “classic” 90-degree tibial bone cut is typically made by the surgeon simply approximating the 90-degree angle. Therefore, the usual cut made to the tibia in TKA is not necessarily ideal and is made by approximation. Thus, improvements to the angle and precision of the tibial cut may improve the ligament balancing and overall result of a TKA procedure.

Currently available systems that attempt to improve tibial bone cuts during knee surgery fall into three broad categories: intramedullary, extramedullary, and computer-assisted navigation systems. Intramedullary systems attach to the tibia via a large, intramedullary rod. The main drawback with these systems is that the intramedullary tod is rather large, and thus causes damage to the tibia when inserted. This damage may increase the risk of embolic complications post-surgery. Intramedullary rod systems also have decreased repeatability in patients with bone deformities. Extramedullary systems use an external rod for visualizing and positioning a cutter. They usually attach and are adjusted near the distal end of the tibia, however, so they are adjusted at the end of the tibia opposite the end being cut. Furthermore, since the extramedullary rod is located apart from the actual tibia, there may be visual distortion and difficulty visualizing a midline or landmarks for guiding adjustment of the system. Computer navigation systems are more accurate and less damaging than the other two alternatives, but they are very expensive and more complicated to use, typically requiring more operating room time.

Therefore, a need exists for improved devices, systems and methods for enhancing TKA surgery and specifically for enhancing and/or facilitating the positioning of one or more tibial bone cuts made during a TKA procedure to accommodate a tibial prosthetic. Ideally, such devices, systems and methods would allow a physician to effectively select an angle at which to make a tibial bone cut and would help the physician more accurately make the cut at the selected angle. Such devices, systems and methods would also ideally be simple to use in conjunction with cutting guides, saw blades or burs, robotic and navigational systems, and/or any other equipment used by a surgeon in a TKA procedure. At least some of these objectives will be met by various embodiments of present invention.

SUMMARY OF THE INVENTION

The present invention relates to knee arthroplasty apparatus and method. The present invention provides devices, systems and methods for positioning a bone cut which may be a bone cut on a tibia as part of a TKA or other knee surgery procedure. These devices, systems and methods generally help a physician achieve balancing of ligaments during the knee surgery procedure, thus potentially enhancing the outcome of the procedure and/or reducing wear and tear of an artificial knee joint implanted during the procedure.

In one aspect, a method for positioning a bone cutting guide may involve coupling a cutting guide positioning apparatus with a tibia, adjusting the positioning apparatus in a varus/valgus orientation, adjusting the positioning apparatus in an anterior/posterior orientation, adjusting the positioning apparatus up or down to select a tibial bone resection level, and contacting a cutting guide with the tibia, using the adjusted positioning apparatus. In some embodiments, the method may further include emitting light in a linear configuration from the cutting guide positioning device. In such embodiments, adjusting the apparatus in the varus/valgus orientation may involve moving the light to shine along approximately a midline of an anterior surface of the tibia, and adjusting the apparatus in the anterior/posterior orientation may involve moving the light to shine along approximately a midline of a side of the tibia. In one embodiment, the side of the tibia along which light is shone is the medial side. Optionally, this method may further involve swinging a swing arm of the cutting guide positioning apparatus approximately 90 degrees between the steps of adjusting in the varus/valgus orientation and adjusting in the anterior/posterior orientation. One embodiment further involves locking in the varus/valgus orientation before swinging the swing arm.

In some embodiments, the cutting guide is removably coupled with the guide positioning apparatus during the adjusting steps. In some embodiments, the method further includes attaching the cutting guide to the tibia. Optionally, the method may further include removing the positioning apparatus from the tibia and the cutting guide and making at least one cut on the tibia guided by the cutting guide.

In one embodiment, adjusting the positioning apparatus up or down to select a tibial bone resection level involves moving a resection level adjustment member up or down to contact a stylus touching an upper surface of the tibia and extending to a location anterior to and below the upper surface. In the present application, the “upper surface” of the tibia means the superior articular surface (or surfaces) of the tibia before any tibial bone cuts have been made. These superior surfaces are often referred to as the medial and lateral articular surfaces or the medial and lateral facets of the tibia. For the purposes of this application, any of the terms “upper surface,” “articular surface,” “facet” or “extreme proximal end” of the tibia may be used interchangeably. In one embodiment, the location anterior to and below the upper surface is between about 8 mm and about 11 mm below the upper surface, and the upper surface is the lateral articular surface of the tibia.

In some embodiments, coupling the cutting guide positioning apparatus with the tibia involves advancing the at least one hole in the apparatus over at least one reference pin attached to the tibia. In one embodiment, two foot pads of the positioning device are advanced over two reference pins to contact the medial and lateral articular surfaces of the tibia.

In another aspect, a method for positioning a bone cutting guide on a tibia may include: coupling a cutting guide positioning apparatus with a tibia, wherein the positioning apparatus is coupled with a tibial cutting guide; emitting a light from the positioning apparatus; adjusting the positioning apparatus in a varus/valgus orientation to shine the light approximately along a midline of an anterior surface of the tibia; swinging a swing arm of the positioning apparatus approximately 90 degrees to shine the light along a side of the tibia; adjusting the positioning apparatus in an anterior/posterior orientation to shine the light approximately along a midline of the side of the tibia; adjusting the positioning apparatus up or down to select a tibial bone resection level; and attaching the tibial cutting guide to the tibia, using the adjusted positioning apparatus.

In another aspect, a device for positioning a bone cut on a tibia may include: a tibial attachment member; a coupler moveably attached to the tibial attachment member; a rotationally moveable arm rotationally attached to the coupler; a swing arm coupled with the rotationally moveable arm via an axle such that a free end of the swing arm swings from an anterior position to a side position; a light emitting member coupled with the swing arm at or near the free end for emitting light along the tibia; a varus/valgus adjustment member for adjusting the rotationally moveable arm to direct the emitted light approximately along a midline of an anterior surface of the tibia; an anterior/posterior adjustment member for adjusting the coupler in an anterior/posterior orientation relative to the tibial attachment member to direct the emitted light approximately along a midline of a side of the tibia; and a tibial bone resection level adjustment member for selecting a level for resecting the tibia.

In some embodiments, the tibial attachment member may include at least one foot pad for contacting an articular surface of an uncut tibia and at least one hole for passing the attachment member over a reference pin attached to the tibia. In one embodiment, the attachment member includes a medial articular surface footpad having a first hole and a lateral articular surface footpad having a second hole.

In some embodiments, the light emitting member emits light in a linear or planar configuration. The side of the tibia is the medial side in some embodiments, and the swing arm rotates between a first position in which the light shines along the anterior surface of the tibia and a second position in which the light shines along the medial side of the tibia. Alternatively, the lateral side of the tibia may be addressed in other embodiments. Some embodiments may further include a stylet coupled with the tibial attachment member and configured to extend from an upper surface of the tibia to a location anterior to and below the upper surface. This tibial bone resection level adjustment member is adjustable to contact the tibial cutting guide with the stylus at the location. In some embodiments, the device further includes a tibial cutting guide holder, where adjustments of the adjustment members adjust a position of the cutting guide holder.

In another aspect, a system for positioning a tibial cutting guide on a tibia may include a tibial cutting guide and a cutting guide positioning device. The positioning device may include: a tibial attachment member; a coupler moveably attached to the tibial attachment member; a rotationally moveable arm rotationally attached to the coupler; a swing arm coupled with the rotationally moveable arm via an axle such that a free end of the swing arm swings from an anterior position to a side position; a light emitting member coupled with the swing arm at or near the free end for emitting light along the tibia; a varus/valgus adjustment member for adjusting the rotationally moveable arm to direct the emitted light approximately along a midline of an anterior surface of the tibia; an anterior/posterior adjustment member for adjusting the coupler in an anterior/posterior orientation relative to the tibial attachment member to direct the emitted light approximately along a midline of a side of the tibia; a tibial bone resection level adjustment member for selecting a level for resecting the tibia; and a tibial cutting guide holder, where adjustments of the adjustment members adjust a position of the cutting guide holder.

Generally, the tibial cutting guide holder is moveable relative to the rotationally moveable arm to move the tibial cutting guide into contact with the tibia. In some embodiments, the system may further include at least one reference pin for removably attaching the tibial attachment member of the guide positioning device to the tibia. Optionally, the system may further include at least one cutting guide fastener, such as a pin or rod, for attaching the tibial cutting guide to the tibia.

In another aspect, a method for positioning a bone cut on a tibia may involve: coupling a bone cut positioning apparatus with a tibia; adjusting the positioning apparatus in a varus/valgus orientation relative to the tibia; adjusting the positioning apparatus in an anterior/posterior orientation relative to the tibia; and adjusting the positioning apparatus up or down to select a tibial bone resection level. Optionally, the method may further include, before adjusting in the varus/valgus orientation, attaching a laser light emitter to an arm of the positioning apparatus and, before adjusting in the anterior/posterior orientation, detaching the laser light emitter from the arm and reattaching it at or near an opposite end of the arm. In such an embodiment, attaching the emitter to the positioning apparatus activates the emitter such that it can emit laser light, adjusting the apparatus in the varus/valgus orientation comprises moving emitted laser light to shine along approximately a midline of an anterior surface of the tibia, and adjusting the apparatus in the anterior/posterior orientation comprises moving emitted laser light to shine along approximately a midline of a side of the tibia. In some embodiments, the side of the tibia is the medial side.

In one embodiment, coupling the bone cut positioning apparatus with the tibia may involve coupling a tibial attachment member with a proximal end of the tibia and coupling the arm of the positioning apparatus with the tibial attachment member. The arm extends around the tibia approximately 90 degrees from a first end of the arm anterior to the tibia to a second end of the arm lateral or medial to the tibia. In one embodiment, the arm may attach to the tibial attachment member via magnetic connection and the laser light emitter attaches to the arm via magnetic connection.

Also in one exemplary embodiment, the adjusting steps comprise adjusting a screw coupled with a captured ball to move a portion of the positioning apparatus about a pivot. The method may optionally further involve using the positioning apparatus to attach a bone cutting guide to the tibia. In such an embodiment, the method may further involve removing the positioning apparatus from the tibia and the cutting guide and making at least one cut on the tibia guided by the cutting guide.

In another aspect, a method for positioning a bone cut on a tibia may involve: coupling a bone cut positioning apparatus with a tibia; coupling a laser light emitter with the positioning apparatus at or near one end of an arm of the apparatus, such that when the emitter is coupled with the apparatus is emits light; adjusting the positioning apparatus in a varus/valgus orientation to shine the emitted light approximately along a midline of an anterior surface of the tibia; coupling the laser light emitter with the positioning apparatus at or near an opposite end of the arm, such that when the emitter is coupled with the apparatus is emits light; adjusting the positioning apparatus in an anterior/posterior orientation to shine the light approximately along a midline of a side of the tibia; and adjusting the positioning apparatus up or down to select a tibial bone resection level. Optionally, in one embodiment the method may also include attaching a tibial cutting guide to the tibia, using the adjusted positioning apparatus, removing the positioning apparatus from the tibia and the cutting guide, and making at least one cut on the tibia guided by the cutting guide.

In yet another aspect of the present invention, a device for positioning a bone cut on a tibia may include a tibial attachment member, an arm attachable to the tibial attachment member and extending in an arc of approximately 90 degrees, a laser light emitter attachable to the arm at a first position at or near one end of the arm an a second position at or near an opposite end of the arm, a varus/valgus adjustment member for moving the arm to direct light emitted by the emitter in the first position approximately along a midline of an anterior surface of the tibia, an anterior/posterior adjustment member for moving the arm to direct light emitted by the emitter in the second position approximately along a midline of a side of the tibia, and a bone resection level adjustment member for selecting a level for resecting the tibia.

In some embodiments, the tibial attachment member may include independently movable medial and lateral feet for contacting the medial and lateral articular surfaces of the tibia. In one embodiment, the varus/valgus adjustment member comprises a first captured ball and captured screw that rotates the tibial attachment member about a first pivot point, and the anterior/posterior adjustment member comprises a second capture ball and captured screw that rotates the tibial attachment member about a second pivot point. In one embodiment, the laser light emitting member attaches to the arm at the first position and the second position via magnetic force. In this or other embodiments, the arm may attach to the tibial attachment member via magnetic force.

One embodiment may further include a tibial cutting guide holder, wherein adjustments of the adjustment members adjust a position of the cutting guide holder. Some embodiments may further include a depth gauge coupled with the bone resection level adjustment member.

In another aspect of the invention, a system for positioning a bone cut on a tibia may include a tibial cutting guide and a bone cut positioning device. The cutting guide positioning device may include: a tibial attachment member; an arm attachable to the tibial attachment member and extending in an arc of approximately 90 degrees; a laser light emitter attachable to the arm at a first position at or near one end of the arm an a second position at or near an opposite end of the arm; a varus/valgus adjustment member for moving the arm to direct light emitted by the emitter in the first position approximately along a midline of an anterior surface of the tibia; an anterior/posterior adjustment member for moving the arm to direct light emitted by the emitter in the second position approximately along a midline of a side of the tibia; and a bone resection level adjustment member for selecting a level for resecting the tibia.

In one embodiment, the tibial cutting guide holder is moveable relative to the arm to move the tibial cutting guide into contact with the tibia. Optionally, the system may further include at least one reference pin for removably attaching the tibial attachment member of the guide positioning device to the tibia. The system may also include at least one cutting guide fastener for attaching the tibial cutting guide to the tibia. In some embodiments, the laser light emitting member emits light in a linear or planar configuration that may be directed along the tibia. In some embodiments, the laser light emitting member attaches to the arm at the first position and the second position via magnetic force. In some embodiments, the arm attaches to the tibial attachment member via magnetic force. Some embodiments may further include a depth gauge attachable to the cutting guide positioning device. In some embodiments, the depth gauge comprises a slidable member adjustable by moving the bone resection level adjustment member and including at least one indicator to indicate to a user when a desired bone cut level has been reached. In some embodiments, the at least one depth gauge comprises multiple depth gauges provided as a set, each gauge having an indicator at a different depth for facilitating a different bone resection level. For example, in one embodiment, the multiple depth gauges comprise three gauges having indicators at 3 mm, 9 mm and 10 mm of depth. In various embodiments, the indicator on a depth gauge may include but is not limited to an LED, a colored marker, a reflective marker and/or a tactile element.

In another aspect of the present invention, a method for positioning a bone cutting guide on a tibia may involve first coupling a bone cut positioning apparatus with a tibia, the positioning apparatus including a stationary arm for attaching at one end to the tibia, a pivoting arm attached to an opposite end of the stationary arm at a pivot joint, a light emitter, and a stylus. The method may next involve adjusting the positioning apparatus in a varus/valgus orientation to shine a light emitted by the light emitter approximately along a midline of an anterior surface of the tibia. Next, the method may include swinging the pivoting arm about the pivot joint to direct the emitted light along a medial surface of the tibia and adjusting the positioning apparatus in an anterior/posterior orientation to shine the light approximately along a midline of the medial surface. Then, the method may include contacting the stylus with a proximal end of the tibia to select a cutting depth for a bone cut to be made on the tibia, where the stylus is coupled with the bone cutting guide. Finally, the method may include attaching the bone cutting guide to the tibia in a position determined by the positioning apparatus.

In some embodiments, coupling the positioning device with the tibia involves attaching a tibial attachment portion of the apparatus with the tibia, where one end of the stationary arm is attached to the tibial attachment portion. In some embodiments, the method may further include removing the positioning apparatus from the tibia and the cutting guide and making at least one cut on the tibia guided by the cutting guide. In some embodiments, coupling the positioning apparatus with the tibia may involve coupling a tibial attachment portion of the apparatus with a pin inserted in the tibia. Optionally, such a method may further include, before adjusting the varus/valgus orientation, rotating the tibial attachment portion about the pin to direct the emitted light along a desired line on the anterior surface of the tibia and thus position the positioning apparatus in a desired rotational orientation relative to the tibia, and attaching the tibial attachment portion to the tibia using at least one additional pin.

In some embodiments, contacting the stylus with the proximal end of the tibia may involve sliding a depth selection member coupled with the positioning apparatus down until the stylus contacts the tibia, where the depth selection member is coupled with the stylus and the cutting guide. In some embodiments, the method may further include selecting a 3 mm cutting depth orientation or a 9 mm cutting depth orientation of the stylus before the contacting step. Optionally, the method may also include locking the pivoting arm relative to the stationary arm before at least one of the adjusting steps, to prevent unwanted movement of the pivoting arm during adjusting. For example, in one embodiment, locking the pivoting arm may involve inserting a locking pin into a first hole on the pivoting arm and a second hole on the stationary arm to lock the pivoting arm in a first position before the varus/valgus adjustment step. Such an embodiment may further involve unlocking the pivoting arm before the swinging step, by removing the locking pin, and inserting the locking pin into a third hole on the pivoting arm and the second hole on the stationary arm to lock the pivoting arm in a second position before the anterior/posterior adjusting step. In some embodiments, each of the adjusting steps may involve turning a separate adjustment screw on the positioning apparatus.

In another aspect of the present invention, a device for positioning a bone cutting guide on a tibia may include: a tibial attachment member including a varus/valgus adjustment member, an anterior/posterior adjustment member, and at least one aperture for coupling with a pin inserted into the tibia; a stationary arm fixedly attachable to the tibial attachment member at one end and extending to a pivot joint at an opposite end; a pivoting arm movably attached at one end to the stationary arm at the pivot joint; a light emitter attachable to the pivoting arm at or near an end of the pivoting arm opposite the pivot joint; a depth selection member movably coupled with the stationary arm and configured to removably attach to the bone cutting guide; and a stylus removably attachable to the bone cutting guide for contacting the tibia to help select a cutting depth.

In one embodiment, the adjustment members of the tibial attachment member may be screws, and the tibial attachment member may include three apertures for allowing passage of three tibial attachment pins therethrough. In one embodiment, the varus/valgus adjustment member may include a first captured ball or cylinder and captured screw that rotates the tibial attachment member about a first pivot point, and the anterior/posterior adjustment member may include a second capture ball or cylinder and captured screw that rotates the tibial attachment member about a second pivot point.

In some embodiments, the light emitter may be a laser light emitter. In some embodiments, the light emitter may attach to the pivoting arm via magnetic force. Optionally, some embodiments may further include a locking pin for locking the pivoting arm in position relative to the stationary arm. In some embodiments, the pivoting arm includes two apertures and the stationary arm includes one aperture, all of which are used to lock the pivoting arm in one of two possible locking positions relative to the stationary arm, using the locking pin. In some embodiments, the pivoting arm may be configured to swing about the pivot joint in an arc of approximately 270°, such that the light emitter can swing from a first position, in which it directs light at an anterior surface of the tibia, to a second position, in which it directs light at a medial surface of the tibia.

In some embodiments, the depth selection member may be coupled with the stationary arm via a first magnet, and the stylus may be coupled with the bone cutting guide via a second magnet. In some embodiments, the stylus may have two oppositely directed points, one for selecting a 3 mm cutting depth and the other for selecting a 9 mm cutting depth. In other embodiments, the stylus may have two oppositely directed points, one for selecting a 3 mm cutting depth and the other for selecting a 10 mm cutting depth.

In another aspect of the present invention, a system for positioning a bone cutting guide on a tibia may include at least one bone cutting guide positioning device and an adjustment device for adjusting the adjustment members. The bone cutting guide positioning device may include: a tibial attachment member including a varus/valgus adjustment member, an anterior/posterior adjustment member, and at least one aperture for coupling with a pin inserted into the tibia; a stationary arm fixedly attachable to the tibial attachment member at one end and extending to a pivot joint at an opposite end; a pivoting arm movably attached at one end to the stationary arm at the pivot joint; a light emitter attachable to the pivoting arm at or near an end of the pivoting arm opposite the pivot joint; a depth selection member movably coupled with the stationary arm and configured to removably attach to the bone cutting guide; and a stylus removably attachable to the bone cutting guide for contacting the tibia to help select a cutting depth.

In some embodiments, the system may further include at least one bone cutting guide for use with the bone cutting guide positioning device. In some embodiments, the positioning device may include a right tibia positioning device and a left tibia positioning device. Optionally, the system may further include a center pin for attaching to a proximal end of tibia at or near its center and at least one medial or lateral pin for attaching to the proximal end of the tibia medial or lateral to the center pin, wherein the pins are used to attach the tibial attachment member to the tibia. Some embodiments may further include a locking pin for locking the pivoting arm in position relative to the stationary arm.

In one embodiment, the adjustment device may be an Allen wrench. In one embodiment, the light emitter may be a laser light emitter. In one embodiment, the stylus may have two oppositely directed points, one for selecting a 3 mm cutting depth and the other for selecting a 9 mm cutting depth. In an alternative embodiment, the stylus may have two oppositely directed points, one for selecting a 3 mm cutting depth and the other for selecting a 10 mm cutting depth.

For a further understanding of the nature and advantages of the invention, reference should be made to the following description taken in conjunction with the accompanying figures. However, each of the figures is provided for the purpose of illustration and description only and is not intended to limit the scope of the embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a bone cut positioning system coupled with a proximal

end of a tibia, according to one embodiment;

FIG. 1B is a side view of the system and tibia of FIG. 1A;

FIG. 1C is an exploded perspective view of the system of FIGS. 1A and 1B;

FIG. 1D is an exploded view of a portion of the system of FIGS. 1A-1C;

FIGS. 2A-2J illustrate a method for positioning a bone cut using a bone cut positioning system, according to one embodiment;

FIG. 3A is a perspective view of a bone cut positioning system coupled with a proximal end of a tibia, according to an alternative embodiment;

FIGS. 3B and 3C are perspective and posterior views, respectively, of the positioning system of FIG. 3A with the addition of an optional stylet;

FIG. 3D is a perspective view of a tibia with attached cutting guide and tibial bone saw blade in place after positioning of the cutting guide using the positioning system of FIGS. 3A-3C;

FIGS. 4A-4I are various views of a tibial attachment member of a bone cut positioning system according to one embodiment;

FIGS. 5A-5J are various views of a bone cut positioning system according to an alternative embodiment;

FIG. 6 is a side view of a tibial pin positioning adjustment member according to one embodiment;

FIG. 7 is a perspective view of a depth guide of one embodiment of a bone cut positioning system;

FIGS. 8A-8D demonstrate a method for placing guide pins and a guide block using a bone cute positioning system according to one embodiment;

FIGS. 9A-9D are various views of a tibial cut check device according to one embodiment;

FIGS. 10A-10D show a depth gauge device for a bone cut positioning system according to one embodiment;

FIGS. 11A-11E show a depth gauge device for a bone cut positioning system according to an alternative embodiment;

FIG. 12A is a perspective view of a bone cutting guide positioning system according to one embodiment;

FIG. 12B is a perspective view of additional, optional components of the positioning system of FIG. 12A;

FIGS. 13A-13S illustrate a method of using the bone cutting guide positioning system of FIGS. 12A and 12B, according to one embodiment; and

FIGS. 14A-14C are perspective views of the system of FIG. 12A.

DETAILED DESCRIPTION OF THE INVENTION

The devices, systems and methods described below may be used in various embodiments to enhance and/or facilitate a total knee arthroplasty (TKA) procedure, a partial knee arthroplasty procedure, or any other suitable knee surgery procedure in which one or more cuts are made on a tibia, typically a proximal end of a tibia. Generally, the embodiments described herein provide a means for positioning a bone cut on a tibia. Although the following description may frequently refer to TKA procedures, the described embodiments may also be used for partial knee arthroplasty procedures or other knee procedures in which tibial bone cuts are made.

Referring to FIG. 1A, one embodiment of a bone cut positioning system 100 is shown attached to a tibia T. In this view, the tibia T is of a right leg and is in an anterior (front) facing orientation, with the lateral side L of the tibia T toward the left side of the figure and the medial side M of the tibia toward the right side of the figure.

FIG. 1B shows system 100 in place with the medial side M of the tibia T facing out of the page and the system 100 rotated to address the medial side M, as will be explained in more detail below. FIG. 1C shows an exploded view of system, and FIG. 1D shows an exploded view of part of system 100.

In the embodiment of FIGS. 1A-1D, system 100 for enhancing and/or facilitating positioning a bone cut on a tibia T includes a bone cutting guide 112 (or “guide block”) and a bone cut positioning device 110. In alternative embodiments, positioning device 110 may be adapted to position a bone cut without using cutting guide 112, or by using a different variation of cutting guide 112. In various embodiments, bone cutting guide 112 may be any currently available or subsequently developed bone cutting guide 112. Because bone cutting guides or guide blocks are well known in the art, they will not be described further herein. In various embodiments, bone cutting guide 112 may be provided as part of the system 100 or alternatively may be available separately.

In some embodiments, bone cut positioning device 110 may be coupled to the tibia T via a tibial reference pin 102 (or “tibial pin”) inserted into the tibia T. Pin 102 may be part of system 100 or may be available separately, in various embodiments. Pin 102 may be used in place of extramedulary rods.

In the embodiment of FIGS. 1A-1D, bone cut positioning device 110 includes a number of component parts, some of which may be more easily viewed in FIGS. 1C and 1D. As shown in FIG. 1D, for example, positioning device 110 may include a tibial attachment member 114 that attaches directly to the tibia T via a hole 115 for accepting pin 102 and is rotationally moveable relative to the tibia T during use of positioning device 110. In this embodiment, tibial attachment member 114 includes two foot pads—a right foot pad 114 a and a left footpad 114 b—for contacting the proximal end of the tibia T. In alternative embodiments, one foot pad or more than two foot pads may be used. Positioning device 110 also includes a coupler 106, which attaches a rotationally moveable arm 128 to tibial attachment member 114. A varus/valgus adjustment member 116 and an anterior/posterior adjustment member 104 (or “tibial slope adjustment member”) move members 128 and 106 relative to the tibial attachment member 114 to adjust the orientations of device 110 and thus adjust the orientation of cutting guide 112 relative to the tibia T. In the embodiment shown, adjustment members 116, 104 are threaded, bolt-like apparatus that are adjustable by an adjustment device 124, such as but not limited to the Allen wrench shown in the figure. In alternative embodiments, any other suitable adjustment apparatus may be used for adjusting coupler 106 relative to tibial attachment member 114, such as rack and pinion gears, ring and pinion gears or the like.

Rotationally moveable arm 128 may be rotated during a positioning process by adjusting adjustment member 116, though rotationally moveable arm 128 remains anterior to the tibia T during the positioning procedure. Rotationally moveable arm 128 includes a slot 108 for receiving a tibial bone resection level adjustment member 132, which is coupled with a cutting guide attachment member 134, which in turn is removably coupled with cutting guide 112. In one embodiment, tibial bone resection level adjustment member 132 may comprise a bolt-like apparatus with threads and an adjustment knob, as pictured in FIGS. 1A-ID. Slot 108 is configured to allow resection level adjustment member 132 to slide horizontally back and forth to move cutting guide 112 toward and away from the tibia T and to move vertically up and down to select a height (i.e., bone resection level) at which cutting guide 112 will create a bone resection plane to be established by a saw blade upon the tibia T. In some embodiments, resection level adjustment member 132 may be locked or set at a desired level after adjustment.

Rotationally moveable arm 128 is coupled with a swing arm 126 (or “swivel arm”) at a pivot point via an axle 129. Optionally, a lock screw 130 may be included to lock swing arm 126 relative to rotationally moveable arm 128, typically in either a 0° (facing anterior tibia) or a 90° (facing side tibia) orientation. Swing arm 126, in turn, is coupled with a light emitting apparatus 120, generally including a light source and in some embodiments an on/off switch 121. Light emitting apparatus 120 is capable of directing a plane of light 122 (FIGS. 1A and 1B) toward a surface of a tibia T for guiding orientation and adjustment of device 110. In alternative embodiments, the light emitted by light emitting apparatus may be in the form of a beam, fan, or any other suitable linear configuration for shining along a length of a tibia. In some embodiments, light emitting apparatus 120 may be tilted by a user to ensure that the plane of light 122 is directed along the tibial surface.

Swing arm 126 may be configured to rotate from the 0° position toward either side to the 90° position. In one embodiment, for example, swing arm 126 may be rotated from the 0° position to a 90° position facing a medial side of a tibia on a first knee of a patient and may be rotated in the opposite direction on the second knee of the patient so that the 90° position also faces the medial side of that second tibia. In alternative embodiments, the 90° position may be either a medial side or a lateral side of a tibia.

Coupler 106 may be adjusted in the anterior/posterior orientation via adjustments to an anterior/posterior adjustment member 104. In various embodiments, coupler 106 may be locked in the anterior/posterior orientation as well as or alternative to locking in the varus/valgus orientation. In some embodiments, adjustment members 116, 104 and locking member 118 may all be screws, bolts or other threaded adjustment members. In the embodiment shown, adjustment members 116, 104 and locking member 118 are adjusted using Allen wrench 124, although in alternative embodiments any suitable adjustment device may be used, such as a screw driver, wrench, fingers or the like.

Referring to FIGS. 1C and 1D, tibial bone resection adjustment member 132 passes through slot 108 and attaches to cutting guide attachment member 134. Cutting guide attachment member 134 is configured as a platform for holding cutting guide 112. In alternative embodiments, attachment member 134 may have any other suitable shape, size or configuration for removably coupling with one or various different cutting guides.

The various components of bone cut positioning device 110 may be manufactured from any suitable materials. For example, in some embodiments many of the components may be made of stainless steel or other metal, which other components may be plastic. In a typical embodiment, all materials of device 110 may be sterilizable by commonly used sterilization techniques, such as gamma irradiation, EtO sterilization and the like. Any adjustment screws, bolts, trunions or the like may be substituted with similar adjustment means in alternative embodiments, and adjustment devices such as Allen wrenches, screw drivers and the like may be likewise substituted.

Referring now to FIGS. 2A-2J, a method is shown for positioning a bone cut on a tibia as part of a TKA or other knee surgery procedure according to one embodiment. As shown in a perspective view in FIG. 2A, bone cut positioning system 100 (bone cut positioning device 110 and cutting guide 112) may first be coupled with the tibia T via reference pin 102. When initially attached, bone cut positioning device 110 may be adjusted such that swing arm 126 positions light emitting device 120 at the 0° angle, i.e., facing the anterior surface of the tibia T. Plane of light 122 may be generally directed toward the anterior surface of the tibia T but may not be initially aligned to shine directly along the midline of the anterior surface.

As shown in FIGS. 2B and 2C, adjustment device 124 may be used to adjust varus/valgus adjustment member 116, which in turn moves rotationally moveable arm 128, swing arm 126 and light emitting member 120 in the varus/valgus orientation. This movement adjusts the direction of plane of light 122 such that, as shown in FIG. 2C, light 122 may be directed approximately along a midline of the anterior surface of the tibia T. Positioning device 110 is configured such that when plane of light 122 is directed along approximately the midline of the anterior surface of the tibia T, as in FIG. 2C, cutting guide 112 is oriented in a desirable varus/valgus orientation for making a tibial bone cut.

In one embodiment, and with reference now to FIG. 2D, adjustment device 124 may next be used to lock in the varus/valgus adjustment of positioning device 110 via locking member 118. In alternative embodiments, it may not be necessary to lock in the varus/valgus adjustment or the adjustment may be locked in automatically by an automatic locking mechanism of device 110.

Referring to FIG. 2E, adjustment device 124 may next be coupled with anterior/posterior adjustment member 104. As shown in FIG. 2F, swing arm 126 may be rotated about axle 129 (now visible) approximately 90° to position light illuminating member 120 to direct plane of light 122 along the medial side M of the tibia T. Although in an alternative embodiment the lateral side L of the tibia T may be used for the bone cut positioning method, the medial side M is generally the preferred side for orienting and positioning device 110 and cutting guide 112.

As shown in FIG. 2G, adjustment device 124 may next be used to adjust anterior/posterior adjustment member 104 (not visible) and thus move coupler 106, rotationally moveable arm 128, swing arm 126 and light emitting member 120 to direct plane of light 122 approximately along the midline of the medial side M of the tibia T. As seen when comparing FIGS. 2F and 2G, as positioning device 110 is adjusted, cutting guide's 112 orientation relative to the tibia is also adjusted. In one embodiment, the anterior/posterior orientation may be locked in place via a second locking member. However, this second locking is optional and is not included in the embodiment shown in the figures.

Referring now to FIG. 2H, once varus/valgus and anterior/posterior adjustments have been made, tibial bone resection level adjustment member 132 may turned to move cutting guide 112 up or down relative to the tibia T (hollow-tipped arrow shows upward movement). This upward or downward adjustment may be made by the physician, depending on a desired location of the cutting guide relative to the tibia T. Adjustment member 132 may then be slid along slot 108 (not visible) to move cutting guide 112 into contact with the tibia T (solid-tipped arrows show horizontal movement).

Once cutting guide 112 is in contact with the tibia T, it may be attached to the tibia T using one or more bone attachment pins 140 (or “rods”), as shown in FIG. 2I. Finally, as shown in FIG. 21, positioning device 110 may be removed, leaving behind cutting guide 112, which the physician may then use to guide a saw blade to cut off a slice of bone from the proximal end of the tibia T. Once the tibial bone cut is made, cutting guide 112 is removed and the rest of the TKA or other knee surgery procedure is performed. As mentioned above, in alternative embodiments, positioning device 110 may be used to mark or otherwise guide a tibial bone cut, thus removing the need for cutting guide 112. In either case, positioning device 110 helps position tibial bone cuts to enhance ligament balancing during a TKA or other knee surgery procedure, and to assure proper alignment of the tibia to the femur.

Referring now to FIGS. 3A-3C, another embodiment of a system 200 for positioning a tibial bone cut is shown. Many of the features of system 200 are the same or similar to those described above in reference to FIGS. 1A-1D, and thus those features will not be described here again. In this embodiment, as best seen the posterior view of FIG. 3C, a tibial attachment member 213 includes a lateral attachment member 213 a with a lateral footpad 214 b and a medial attachment member 213 b with a medial footpad 214 b. Attachment members 213 a, 213 b are attached to a tibia T via two reference pins 203, and a coupler 206 is attached to attachment members 213 a, 213 b. As shown in FIG. 3A, in some embodiments, attachment members 213 a, 213 b may be locked to coupler 206 using a lock screw 215 or other locking mechanism. As also shown in FIGS. 3A and 3C, coupler may in some embodiments also be attached to the tibia T via another reference pin 202.

System 200 includes an alternative cutting guide holder 234, which includes two rods 235 on which cutting guide 212 rests during adjustments of system 200 to select a desired location for cutting guide 212. As in the previously described embodiment, holder 234 is attached to a bone cut resection level adjustment member 232 configured to move holder 234 up and/or down to select a desired resection level. Adjustment member 232 can also move back and forth through a slot on the rotationally moveable arm, as previously described, to bring cutting guide 212 into or out of contact with the tibia T.

With reference to FIGS. 3B and 3C, in some embodiments, system 200 may include a stylus 250 for determining a bone cut resection level. Stylus 250 is coupled with tibial attachment member 213 and/or coupler 206, according to various embodiments. As seen in FIG. 3C, stylus 250 contacts one of the articular surfaces of the tibia via a tibial contact 254. In the embodiment shown, the lateral articular surface is contacted. As seen in FIG. 3B, stylus 250 wraps around the tibia T and extends to a resection level bumper 252, against which cutting guide 212 may be adjusted to select a desired bone resection level. In this embodiment, wherein tibial contact 254 contacts the lateral articular surface of the tibia T, the contact point of bumper 252 may be between about 8 mm and about 11 mm below the lateral articular surface, and in some embodiments between about 9 mm and about 10 mm below the lateral articular surface. If stylus 250 is instead coupled with a medial articular surface, bumper 252 will likely extend to a different level below the medial articular surface. Generally, stylus 250 is used to help select a desired tibial resection level at which to place cutting guide 212 by adjusting adjustment member 232.

Referring now to FIG. 3D, tibial cutting guide 212 is shown attached to the tibia T via two attachment rods 270 (or “pins”). In alternative embodiments, only one rod 270, more than two rods 270, or any suitable alternative fasteners may be used to attach cutting guide 212 to the tibia T. After cutting guide 212 is attached, a tibial bone saw blade 260 is then used to make the bone cut (or multiple cuts) on the proximal tibia T. Blade 260 is attached to a bone saw (not shown) to make the cut. Once the tibial bone cut is made, cutting guide 212 is removed and the remainder of the TKA or other knee arthroplasty procedure is performed.

Referring now to FIGS. 4A-4H, a tibial attachment member 300 of a tibial bone cut positioning system according to one embodiment is shown. In this embodiment, as shown in FIG. 4A, tibial attachment member 300 includes three fixation holes 302, which are offset relative to one another to provide enhanced stability to attachment member 300 when attached to a tibia. Tibial attachment member 300 may further include two tibial contact feet 304 (FIG. 4C) for contacting medial and lateral articular surfaces of the tibia. These contact feet 304 may be independently movable and/or lockable in some embodiments. Feet 304 may also be designed to slip under the femur and provide consistent contact with the tibia, as shown in FIG. 4B.

FIGS. 4D-4F are top, side and cross-sectional views, respectively, of tibial attachment member 300, showing tibial slope (or “anterior/posterior”) adjustment apparatus 306, 308, 310. In the cross-sectional view of FIG. 4F, adjustment apparatus can be seen to include a captured ball 306, a captured screw 308 and a pivot 310. In this embodiment, captured screw 308 may be adjusted relative to captured ball 306 to move tibial attachment member 300 about pivot 310 and thus adjust the tibial slope (or “anterior/posterior orientation”) of tibial attachment member 300. In alternative embodiments, other adjustment mechanisms may be used, and thus this embodiment is provided as an example only.

FIGS. 4G-4I are top, side and cross-sectional view, respectively, of tibial attachment member 300, showing varus/valgus (or “medial/lateral”) adjustment apparatus 312, 314, 316. In the cross-sectional view of FIG. 4I, taken through dotted line A-A in FIG. 4H, adjustment apparatus can be seen to include a captured ball 312, a captured screw 314 and a pivot 316, similar to the adjustment apparatus for tibial slope. Again, captured screw 314 may be adjusted relative to captured ball 312 to move tibial attachment member 300 about pivot 316 and thus adjust the varus/valgus (or “anterior/posterior”) orientation of tibial attachment member 300. Again, in alternative embodiments, other adjustment mechanisms may be used.

Referring now to FIGS. 5A-5I, an alternative embodiment of a tibial bone cut positioning system 320 is shown in various views. As shown in FIG. 5A, in one embodiment, bone cut positioning system 320 may include a tibial attachment member 322 removably couplable with an arm 328. Attachment member 322 and arm 328 may be coupled with one another via any acceptable means in various embodiments. For example, in the embodiment shown, attachment member 322 may include a magnetic attachment plate 324 that mates with a magnetic attachment plate on arm 328. Pins 326 on the magnetic attachment plate of arm 328 may fit into holes on the magnetic attachment plate 324 of attachment member 322. This configuration may facilitate removal and attachment of arm 328 to attachment member 322, thus making the overall system 320 less cumbersome and easier to use.

Turning now to FIG. 5B, arm 328 generally includes a first attachment point 330 a and a second attachment point 330 b for removably attaching a laser light emitter 340 (FIG. 5C) to arm 328. As shown, arm 328 generally extends approximately 90 degrees about an arc, although arm 328 itself need not be shaped as an arc. Attachment points 330 a, 330 b are located at or near opposite ends of arm 328, so that when arm 328 is attached to tibial attachment member 322, attachment points 330 a, 330 b are generally positioned so that an attached laser light emitter 340 will address anterior and side aspects of a tibia (either medial or lateral). Attachment points 330 a, 330 b may attach with laser light emitter 340 via magnetic force attachment, similar to the attachment of arm 328 to tibial attachment member 322. In one embodiment, each end of arm 328 may include one attachment point 330 a, 330 b (or “magnetic contact area”), as shown in FIG. 5B. Alternatively, as shown in FIG. 5I, another embodiment of an arm 322 may include attachment points 334 (or “magnetic contact areas”) at each end of arm 322. Alternatively, as shown in FIG. 5J, another embodiment may include magnetic attachment points to a rotational swing arm 126. In yet other embodiments, light emitter 340 may attach to arm 328 via any other suitable attachment means.

FIGS. 5D-5H show laser light emitter 340 attached at various points to arm and emitting light 342 toward a tibia from various angles. In one embodiment, light emitter 340 may not be turned on until it is attached to arm 328 via its magnetic attachment (or other attachment means). This control make act as a safety mechanism to prevent light emitter 340 from being turned on prematurely or from being left on accidentally after use. In one embodiment, light emitter 340 may turn on automatically when attached to arm 328 and turned off automatically when removed from arm 328. The simple removability and attachment of light emitter 340 relative to arm 328 allows for easy movement from tibial slope adjustment to varus/valgus adjustment and vice versa. FIGS. 5E and 5F show varus/valgus alignment positions, and FIGS. 5G and 5H show tibial slope alignment positions.

Turning now to FIG. 6, in one embodiment a bone resection level adjustment member of a bone cut positioning system may include an adjustment knob 344 coupled with a pin template 346 (or “pin guiding member”). Each turn of knob 344 may drop or raise pin template 346 by a known distance, such as 1 mm in one embodiment. As shown in FIG. 7, some embodiments may further include a depth gauge 348, which may reference off of the trough of the medial or lateral compartment of the tibia for helping a user determine a depth of the bone cut to be made.

FIGS. 8A-8D demonstrate a method according to one embodiment for making a bone cut on a tibia using a bone cut positioning system 320. As shown in FIG. 8A, once tibial slope, varus/valgus and bone cut level adjustments have been made via system 320, pins 350 may be inserted through holes on pin template 346 and drilled into the tibia. As shown in FIG. 8B, arm 328 and the components of system 320 attached to arm 328 may be removed from tibial attachment member 322. As shown in FIGS. 8C and 8D, a bone cutting guide 352 may then be advanced over pins 350, and a bone saw 354 may be used to make the tibial bone cut.

Referring now to FIGS. 9A-9D, one optional feature of a bone cut positioning system may be a tibial cut check device 360. In use, cut check device 360 is attached to the cut surface of the tibia, either via pins 350 or by holding manually by a user. Visualization features 362 of cut check device 360 may then be used to assess the tibial cut. As shown in FIG. 9B, cut check device 360 may include an attachment plate 364 so that it can be attached to arm 328 using the same attachment means as tibial attachment device 322. As shown in FIGS. 9C and 9D, laser light emitter 340 can then be used with cut check device 360 coupled with arm 328 to check tibial slope and varus/valgus alignment. If the desired alignments were not achieved with the initial cut, additional cuts may be made and checked again until the desired result is achieved.

With reference now to FIGS. 10A-10D, another optional feature of a bone cut positioning system may be one or more depth gauges 370 for helping a user select a desired tibial bone resection level. In one embodiment, for example, multiple depth gauges 370 for different bone cut resection levels may be provided. As shown, for example, one embodiment may include a 3 mm gauge 372 a, a 9 mm gauge 370 b, and a 10 mm gauge 370 c, for measuring a bone resection level. In this embodiment, each gauge 370 includes an LED 372 at the desired level of bone resection—i.e., a 3 mm LED 372 a, a 9 mm LED 372 b, and a 10 mm LED 372 c.

As shown in FIG. 10B, depth gauge 370 b may be placed into a depth arm 374, which is attached to tibial attachment member 322 and includes an aperture 376. As discussed previously, a pin template 346 is generally included in the bone cut positioning system and is attached to arm 328 and adjustable via knob 344. As shown in FIG. 10C, turning knob 344 will raise pin template 346 to contact one end of depth gauge 370 b. As shown in FIG. 10D, continuing to turn know 344 will continue to raise pin template 346 and thus will push depth gauge 370 b upward, so that LED 372 b will be visible through aperture 376. At this point, when LED 372 b is visible through aperture 376, the user knows the desired depth of bone cut has been reached.

In another embodiment, and with reference now to FIGS. 11A-11E, depth gauges of various heights 380 a, 380 b, 380 c may include colored, reflective or otherwise distinguishable markers 382 a, 382 b, 382 c. Of course, in this or the previous embodiment, any suitable number of depth gauges 380 may be provided, from one to any unlimited number. In some embodiments, multiple depth gauges 380 may be provided as a set or kit, while in other embodiments, depth gauges may be provided individually. Also, although the examples of LEDs 372 are shown in depth gauges 370 a, 370 b, 370 c, and circumferential markers 382 are shown in depth gauges 380 a, 380 b, 380 c, in alternative embodiments any suitable visualization, tactile or other feedback elements may be used to facilitate a user's confirmation that a desired depth has been achieved, such as but not limited to one or more bumps for tactile feedback, colored dots for visualization, or a beeping noise indicating desired depth. Thus, the exemplary embodiments of FIGS. 10A-10D and 11A-11E are provided for exemplary purposes only.

Turning now to FIG. 11B, in this embodiment, as in the previous one, gauge 380 a may be inserted into a depth arm 384 having an aperture 386 (in this embodiment slot-shaped rather than round). As shown in FIGS. 11C and 11D, knob 344 may then be adjusted to bring pin template 346 into contact with one end of gauge 380 a (FIG. 11C) and then to push up gauge 380 a until marker 382 a shows through aperture 386. If the user turns knob 344 too far, as in FIG. 11E, marker 382 b is no longer visible through aperture 386, so user will know to turn knob in the opposite direction to adjust the bone cut height.

Referring now to FIG. 12A, another alternative embodiment of a system 400 for positioning a bone cutting device, typically a guide block (or “cutting guide”), on a tibia during knee surgery is shown. In one embodiment, system 400 may include a bone cutting guide positioning device 401 and one or more cutting guides 432 (or “guide blocks”). Bone cutting guide positioning device 401 may include a tibial attachment member 402, a stationary arm 410 attachable to tibial attachment member 402, a pivoting arm 414 attached to stationary arm 410 via a pivot joint 412, and a light emitter 416 removably attached to a far end of pivoting arm 414. Device 401 may also include a depth selection member 424 and a stylus 426, both of which may be coupled with cutting guide 432. In various alternative embodiments, system 400 may include one or more cutting guides 432 or may be provided by itself, for use with one or more “off the shelf” cutting guides. Optionally, device 401 may also include a locking pin 422, which may be used to lock pivoting arm 414 in place relative to stationary arm 410 by positioning it inside apertures 415 on pivoting arm 414 and stationary arm 410.

Tibial attachment member 402 may include multiple pin apertures 404 a, 404 b, through which pins may be passed to attach tibial attachment member 402 to a tibia. In one embodiment, tibial attachment member 402 may include a center pin aperture 403 (not shown in FIG. 12A but illustrated in FIG. 13B), a medial aperture 404 a and a lateral aperture 404 b. Tibial attachment member 402 may also include a varus/valgus adjustment member 406 and an anterior/posterior adjustment member 408. The adjustment members 406, 408 are described in further detail below, in reference to an exemplary method for using system 400. In various embodiments, tibial attachment member 402 may be either permanently or removably attached to stationary arm 410.

Stationary arm 410 may include a magnetic plate 411 disposed in a posterior recess, along which depth selection member 424 may slide up and down for selecting a desired cutting depth. In an alternative embodiment, magnetic plate 411 may be made of a metallic material, and an anterior surface of depth selection member 424 may be made of a magnetic material, so that the two components may attach together via magnetic forces. In alternative embodiments, depth selection member 424 may be permanently attached to stationary arm 410 or may be removably or permanently attached to tibial attachment member 402 in a way that allows for cutting depth selection. Stationary arm 410 extends from one end attached to tibial attachment member 402 to pivot joint 412 at the opposite end. In some embodiments, stationary arm 410 further includes an aperture (not visible in FIG. 12A) for allowing passage of locking pin 422. Stationary arm 410 may be made of any suitable material and by any suitable manufacturing process. In one embodiment, for example, stationary arm 410 and pivoting arm 414 are both plastic, injection molded parts. These and other components of system 400 may be fully disposable in some embodiments or reusable and sterilizable in other embodiments.

Pivoting arm 414 is attached at one end to stationary arm 410 via pivot joint 412 and at an opposite end to light emitter 416. In one embodiment, pivoting arm 414 may be configured to swing around pivot joint 412 approximately 270°, so that it can position light emitter 416 in a first (or “anterior facing”) position to shine light onto an anterior surface of a tibia and then swing around to position light emitter 416 in a second (or “medial facing”) position to shine light onto a medial surface of the tibia. In alternative embodiments, pivoting arm may be designed to swing through a smaller or larger arc, such as between about 180° and about 360°. In some embodiments, pivoting arm 414 includes two apertures 415, through which locking pin 422 may be passed to enter an aperture on stationary arm 410 and thus lock pivoting arm 414 in the anterior facing or medial facing position, relative to stationary arm 410. For convenience, locking pin 422 may be coupled with pivot joint 412 or any other portion of device 401 via flexible tether 420, which in alternative embodiments may be a band, string, or the like. This locking function helps prevent unwanted movement of pivoting arm 414 during adjustment of tibial attachment member 402.

In one embodiment, bone cutting guide positioning device 401 is configured to be “side specific.” In other words, one positioning device 401 is used for a tibia of a left leg, and another positioning device 401 is used for a tibia of a right leg. In the embodiment shown and described in this and subsequent figures, for example, positioning device 401 is configured for positioning a cutting guide on a tibia of a left leg. In alternative embodiments, it may be possible that device 401 is “ambidextrous,” or usable on either a left leg or a right leg. The embodiment shown and described herein is also configured such that pivoting arm 414 swings toward a medial side of the leg/tibia, to position light emitter 416 to emit light onto a medial side of the tibia. This feature was designed according to typical surgeon preference of referencing the medial side of the tibia for bone cut positioning purposes. In an alternative embodiment, however, device 401 may be configured such that pivoting arm 414 swings toward a lateral side of the leg/tibia, to position light emitter 416 to emit light onto a lateral side of the tibia.

Light emitter 416 may be fixedly or removably attached to one end of pivoting arm 414. In the embodiment shown, light emitter 416 is removably attached via a magnetic attachment 418. In one embodiment, magnetic attachment 418 may trigger a switch in light emitter 416, such that when light emitter 416 is attached to pivoting arm 414, light emitter 416 automatically turns on and emits light. Light emitter 416 may be a laser light emitter in one embodiment, emitting a line or plane of light that may be directed in a straight line along a surface of a tibia. In alternative embodiments, light emitter 416 may be an LED or any other light emitting device, as listed and described in relation to other embodiments above. Light emitter 416 may include a housing made of plastic or any other suitable material.

As mentioned above, depth selection member 424 may be removably coupled with stationary arm 410 in recess 411, cutting guide 432 may be removably coupled with a platform 425 of depth selection member 424, and stylus 426 may be removably coupled with cutting guide 432. In one embodiment, a top surface of cutting guide 432 may be metallic, and stylus 426 may be attached to this metallic surface at any desired location via a magnet on stylus 426. In alternative embodiments, the components may be attached to one another in different ways. For example, stylus may be coupled with depth selection member 424 directly.

Stylus 426, in one embodiment, may be a two-sided stylus, allowing for selection of either of two different cutting depths. For example, some surgeons prefer to reference a “worst” or “most worn” side of a proximal tibia when positioning a tibial bone cut, and may try to cut approximately 3 mm below the level of the most worn surface. Other surgeons prefer to reference a “best” or “least worn” side of the proximal tibia and try to position a bone cut approximately 9 mm or approximately 10 mm below the surface of that side. Thus, stylus 426 may be flipped to one side to use a 3 mm point 428 if desired, or may be flipped to an opposite side to use a 9 mm point 430 (or in an alternative embodiment a 10 mm point). Alternative embodiments may have points with different depth measurements, such as about 2 mm, about 4 mm, about 8 mm, about 11 mm, etc.

Although many of the various components of device 401 have been described above as being removably attachable with one another, in alternative embodiments, any (or even all) components may be permanently attached to one another. Cutting guide 432 typically is the only component which should not be permanently attached to device 401, since part of the method of using device 401 typically includes removing device 401 from cutting guide 432 to leave cutting guide 432 in place on the tibia. Device 401 is generally defined not to include cutting guide 432. Instead, cutting guide 432 is an optional component of system 400.

Referring now to FIG. 12B, in some embodiments, system 400 may further include an adjustment device 440 for adjusting tibial attachment member 402, and multiple pins 444, optionally housed in a pin pack 442. Adjustment device 440 may be an Allen wrench (as shown) or alternatively a screw driver or other tool for turning adjustment members 406, 408. Pins 444 may be provided for attaching tibial attachment member 402 to a tibia and/or for attaching cutting guide 432 to a tibia. In other embodiments, adjustment device 440 and/or pins 444 may not be provided as part of system 400.

FIGS. 13A-13S illustrate one embodiment of a method for using bone cutting guide positioning system 400 to position a bone cutting guide on a tibia T. As shown in FIG. 13A, in this embodiment, a first step may involve driving a centering pin 450 into a proximal end of a tibia T, approximately at a center point 452. Centering pin 450 may be any standard pin or may be provided as part of system 400, and it may be driven into the tibia T via standard means, such as drilling a hole in the tibia and advancing pin 450 into the hole.

As shown in FIG. 13B, once centering pin 450 is placed in the tibia T, tibial attachment member 402 of bone cutting guide positioning device 401 may be slid over pin 450 to contact the proximal end of the tibia T (illustrated by large arrows). Tibial attachment member 402 includes a center aperture 403 for sliding over pin 450. In the embodiment shown, stationary arm 410, pivoting arm 414 and light emitter 416 are attached to tibial attachment member 402 when it is advanced over centering pin 450, and light emitter 416 is on and emitting a band of light 454. In an alternative embodiment, tibial attachment member 402 may be slid onto centering pin 450 first, by itself, and then stationary arm 410 may be attached to it. In the embodiment shown, pivoting arm 414 is locked, via locking pin 422, in an anterior facing position relative to stationary arm 410. This means that when device 401 is first slid onto centering pin 450, band of light 454 will point toward an anterior surface of the tibia T.

Turning now to FIG. 13C, tibial attachment member 402 may next be rotated clockwise and/or counterclockwise about center pin 450 (solid, curved arrows) to align device 401 in a desired rotational orientation. To determine when a desired rotational orientation is achieved, a surgeon may use emitted band of light 454 and rotate tibial attachment member 402 until light 454 is aligned in a desired position relative to one or more landmarks on the tibia T.

Once a desired rotational orientation is achieved, and with reference now to FIG. 13D, two additional fixation pins 456 may be driven through medial aperture 404 a and lateral aperture 404 b of tibial attachment member 402 to secure tibial attachment member 402 to the tibia T. In alternative embodiments, one fixation pin 456 may be used instead of two, or more than two fixation pins 456 may be used.

Referring now to FIGS. 13E and 13F, the next step in an exemplary method may be to use adjustment device 440 to adjust varus/valgus adjustment member 406 of tibial attachment member 402, which adjusts an angle of device 401 in a varus/valgus orientation. Adjustment device 440 can be turned in a clockwise direction (as shown by curved arrow) or counterclockwise direction, which will make tibial attachment member 402 tilt toward the medial side or the lateral side of the tibia T. For example, as shown in FIG. 13F, adjustment device 440 may be turned clockwise, which may cause tibial attachment member to tilt up on the lateral side, thus causing band of light 454 to move toward the midline of the anterior surface of the tibia T. A surgeon can thus adjust varus/valgus or medial/lateral tilt of device 401 to achieve a desired orientation, which will translate to a desired orientation of a cutting guide in the varus/valgus orientation.

Turning next to FIGS. 13G and 13H, a next step of the method may involve removing locking pin 422 from a first aperture 415 a on pivoting arm 414 and an aperture 460 on stationary arm 410. Removal of locking pin 422 is illustrated in FIG. 13G, but first aperture 415 a and aperture 460 are visible on FIG. 13H. Next, as shown in FIG. 13H, pivoting arm 414 may be swung around pivot joint 412 approximately 270° to a medial facing position, such that light emitter 416 faces a medial surface M of the tibia T.

Referring now to FIGS. 131 and 13J, once device 401 is oriented so that light emitter 416 faces the medial surface M of the tibia T, a surgeon/user may use adjustment device 440 to adjust anterior/posterior adjustment member 408, to select a desired anterior/posterior orientation (or “tibial slope”) for the bone cut to be made to the tibia T. Adjustment device 440 may be turned clockwise or counterclockwise. In the embodiment shown, a counterclockwise adjustment (curved arrow at the top of FIG. 13J) changes the orientation of tibial attachment member 402 such that the slope becomes more anterior. In other words, the anterior side of tibial attachment member 402 becomes lower relative to its posterior side when anterior/posterior adjustment member 408 is turned in a counterclockwise direction. The opposite occurs if adjustment member 408 is turned in a clockwise direction. Of course, in an alternative embodiment, clockwise and counterclockwise adjustments may have the opposite effects. When anterior/posterior adjustment member 408 is adjusted, it causes tibial attachment member 402 to tilt, thus moving beam of light 454, as shown in FIG. 13J. A surgeon may adjust device 401 in this anterior/posterior or tibial slope orientation until a desired position of light 454 is achieved. This will translate to a desired tibial slope of the bone cut when it is made.

Referring to FIGS. 13K and 13L, now that the varus/valgus and anterior/posterior adjustments have been made, the surgeon user may attach a vertical shaft 419 of depth selection member 424 to stationary to stationary arm 410 via magnetic plate 411. Vertical shaft 419 may have a metallic surface (not visible) facing magnetic plate 411, so that they will attach together. Cutting guide 432 may slide onto platform 425 (not visible) of depth selection member 424 and may include a metallic upper surface 413. Stylus 426 may include a magnetic surface 417 on each side (bottom side not visible), so that either side may be coupled with metallic upper surface 413. One of the two sides 428, 430 of stylus 426 may be chosen before attaching it to cutting guide 432, as shown in FIG. 13L. At this point, depth selection member 424, stylus 426 and cutting guide 432 are ready to be moved/adjusted into position.

With reference now to FIG. 13M, once depth selection member 424 is attached to cutting guide positioning device 401, with stylus 426 and cutting guide 432 attached to it, depth selection member 424 may be adjusted up and/or down to contact the selected tip 428 with a proximal surface of the tibia T (or “tibial plateau”). For example, if the 3 mm tip 428 is selected, when tip 428 contacts the desired tibial surface, device 401 positions cutting guide 432 at a location to create a bone cut having a depth 429 of approximately 3 mm. If the 9 mm tip 430 were chosen, device 401 would provide a bone cut of approximately 9 mm. In other embodiments, other bone cutting depths may be selected. Adjustment of depth selection member 424 may be made by sliding vertical shaft 419 up and down relative to stationary arm 410.

Referring now to FIGS. 13N and 13O, once cutting guide 432 is in a desired position relative to the tibia T, pins 444 may be drilled through two cutting guide holes 433 to attach cutting guide 432 to the tibia T. Any holes 433 may be used for this purpose, such as those illustrated in the figures. As seen best in FIG. 13O, cutting guide 432 typically includes a slot 435 between upper surface 413 and the body of guide 432. A bone saw may generally be positioned in slot 435 or on top of upper surface 413 to make a bone cut.

As shown in FIG. 13P, all components of system 400, other than cutting guide 432 and pins 444, may next be removed from the tibia T. If necessary, as shown in FIGS. 13Q and 13R, cutting guide 432 can be adjusted so that pins 444 pass through different holes. It may be desired, for example, to move cutting guide 432 up if a bone saw blade 437 is to be passed through slot 435 (FIG. 13Q) or to move cutting guide 432 down if bone saw blade 437 is to rest on top of upper surface 413 (FIG. 13R).

Finally, as illustrated in FIG. 13S, a bone saw 490 may be used with cutting guide 432 to make a bone cut on the proximal tibia T. In the example shown, saw blade is being used through slot 435. As already mentioned, in alternative embodiments, saw blade 437 may be used on top of upper surface 413.

Referring now to FIGS. 14A-14C, various views of bone cutting guide positioning system 400 are shown. FIG. 14A is a partially exploded view, showing the various components of system 400 separated from one another. FIGS. 14B and 14C show system 400 fully assembled. As mentioned previously, in various alternative embodiments, one or more components of system 400 that have been described above as being removably attached may be permanently attached. Also, bone cutting guide positioning device 401 has generally been described herein as including tibial attachment member 402, stationary arm 410, pivot joint 412, pivoting arm 414, light emitter 416, depth selection member 424 and stylus. In alternative embodiments, the device may include fewer of these components or may include additional components, such as cutting guide 432. In one embodiment, cutting guide 432, pins 444, 450, 456 and adjustment device 440 are considered part of system 400 rather than as part of device 401. Generally, the terms “device” and “system” should not be interpreted as limiting the scope of the invention as it is defined in the claims.

The present invention may be embodied in other specific forms without departing from the essential characteristics thereof. For example, in alternative embodiments method steps may be deleted, added or performed in a different order than that described above. In one embodiment, for example, it may be possible to perform the anterior/posterior adjustment prior to the varus/valgus adjustment. In another alternative embodiment, it may be possible to use the lateral side of the tibia rather than the medial side for anterior/posterior adjustment. Thus, the embodiments described above as well as alternative embodiments and equivalents are intended to be included within the scope of the present invention, which is set forth in the following claims. While the description has been geared to work with a tibia, the device, method and system may be used with other bones. All elements and steps described are preferably included but may be omitted or replaced with other elements and steps. 

What is claimed is:
 1. A method for positioning a bone cutting guide on a tibia, the method comprising: coupling a bone cut positioning apparatus with a tibia, the positioning apparatus including a stationary arm for attaching at one end to the tibia, a pivoting arm attached to an opposite end of the stationary arm at a pivot joint, a light emitter, and a stylus; adjusting the positioning apparatus in a varus/valgus orientation to shine a light emitted by the light emitter approximately along a midline of an anterior surface of the tibia; swinging the pivoting arm about the pivot joint to direct the emitted light along a medial surface of the tibia; adjusting the positioning apparatus in an anterior/posterior orientation to shine the light approximately along a midline of the medial surface; contacting the stylus with a proximal end of the tibia to select a cutting depth for a bone cut to be made on the tibia, wherein the stylus is coupled with the bone cutting guide; and attaching the bone cutting guide to the tibia in a position determined by the positioning apparatus.
 2. A method as in claim 1, wherein coupling the positioning device with the tibia comprises a tibial attachment portion of the apparatus with the tibia, wherein one end of the stationary arm is attached to the tibial attachment portion.
 3. A method as in claim 1, further comprising: removing the positioning apparatus from the tibia and the cutting guide; and making at least one cut on the tibia guided by the cutting guide.
 4. A method as in claim 1, wherein coupling the positioning apparatus with the tibia comprises coupling a tibial attachment portion of the apparatus with a pin inserted in the tibia.
 5. A method as in claim 4, further comprising, before adjusting the varus/valgus orientation; rotating the tibial attachment portion about the pin to direct the emitted light along a desired line on the anterior surface of the tibia and thus position the positioning apparatus in a desired rotational orientation relative to the tibia; and attaching the tibial attachment portion to the tibia using at least one additional pin.
 6. A method as in claim 1, wherein contacting the stylus with the proximal end of the tibia comprises sliding a depth selection member coupled with the positioning apparatus down until the stylus contacts the tibia, wherein the depth selection member is coupled with the stylus and the cutting guide.
 7. A method as in claim 1, further comprising selecting a 3 mm cutting depth orientation or a 9 mm cutting depth orientation of the stylus before the contacting step.
 8. A method as in claim 1, further comprising locking the pivoting arm relative to the stationary arm before at least one of the adjusting steps, to prevent unwanted movement of the pivoting arm during adjusting.
 9. A method as in claim 8, wherein locking the pivoting arm comprises inserting a locking pin into a first hole on the pivoting arm and a second hole on the stationary arm to lock the pivoting arm in a first position before the varus/valgus adjustment step.
 10. A method as in claim 9, further comprising: unlocking the pivoting arm before the swinging step, by removing the locking pin; and inserting the locking pin into a third hole on the pivoting arm and the second hole on the stationary arm to lock the pivoting arm in a second position before the anterior/posterior adjusting step.
 11. A method as in claim 1, wherein each of the adjusting steps comprises turning a separate adjustment screw on the positioning apparatus.
 12. A device for positioning a bone cutting guide on a tibia, the device comprising: a tibial attachment member including a varus/valgus adjustment member, an anterior/posterior adjustment member, and at least one aperture for coupling with a pin inserted into the tibia; a stationary arm fixedly attachable to the tibial attachment member at one end and extending to a pivot joint at an opposite end; a pivoting arm movably attached at one end to the stationary arm at the pivot joint; a light emitter attachable to the pivoting arm at or near an end of the pivoting arm opposite the pivot joint; a depth selection member movably coupled with the stationary arm and configured to removably attach to the bone cutting guide; and a stylus removably attachable to the bone cutting guide for contacting the tibia to help select a cutting depth.
 13. A device as in claim 12, wherein the adjustment members of the tibial attachment member comprise screws, and wherein the tibial attachment member includes three apertures for allowing passage of three tibial attachment pins therethrough.
 14. A device as in claim 12, wherein the varus/valgus adjustment member comprises a first captured ball or cylinder and captured screw that rotates the tibial attachment member about a first pivot point, and wherein the anterior/posterior adjustment member comprises a second capture ball or cylinder and captured screw that rotates the tibial attachment member about a second pivot point.
 15. A device as in claim 12, wherein the light emitter comprises a laser light emitter.
 16. A device as in claim 12, wherein light emitter attaches to the pivoting arm via magnetic force.
 17. A device as in claim 12, further comprising a locking pin for locking the pivoting arm in position relative to the stationary arm.
 18. A device as in claim 17, wherein the pivoting arm includes two apertures and the stationary arm includes one aperture, all of which are used to lock the pivoting arm in one of two possible locking positions relative to the stationary arm, using the locking pin.
 19. A device as in claim 12, wherein the pivoting arm is configured to swing about the pivot joint in an arc of approximately 270°, such that the light emitter can swing from a first position, in which it directs light at an anterior surface of the tibia, to a second position, in which it directs light at a medial surface of the tibia.
 20. A device as in claim 12, wherein the depth selection member is coupled with the stationary arm via a first magnet, and wherein the stylus is coupled with the bone cutting guide via a second magnet. 